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Journal Article

#### Ortho-positronium observation in the Double Chooz Experiment

##### MPS-Authors
http://pubman.mpdl.mpg.de/cone/persons/resource/persons30347

Buck,  C.
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons127211

Collin,  A.
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons30570

Haser,  Julia
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons30647

Kaether,  F.
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons30768

Lindner,  M.
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons37603

Reinhold,  B.
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons31154

Wagner,  Stefan
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons37605

Watanabe,  Hideki
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

##### Fulltext (public)

1407.6913.pdf
(Preprint), 311KB

##### Supplementary Material (public)
There is no public supplementary material available
##### Citation

Double Chooz Collaboration, Abe, Y., Anjos, J. C. d., Barriere, J. C., Baussan, E., Bekman, I., et al. (2014). Ortho-positronium observation in the Double Chooz Experiment. Journal of high energy physics: JHEP, 2014(10): 32. doi:10.1007/JHEP10(2014)032.

Cite as: http://hdl.handle.net/11858/00-001M-0000-0025-04A7-E
##### Abstract
The Double Chooz experiment measures the neutrino mixing angle $\theta_{13}$ by detecting reactor $\bar{\nu}_e$ via inverse beta decay. The positron-neutron space and time coincidence allows for a sizable background rejection, nonetheless liquid scintillator detectors would profit from a positron/electron discrimination, if feasible in large detector, to suppress the remaining background. Standard particle identification, based on particle dependent time profile of photon emission in liquid scintillator, can not be used given the identical mass of the two particles. However, the positron annihilation is sometimes delayed by the ortho-positronium (o-Ps) metastable state formation, which induces a pulse shape distortion that could be used for positron identification. In this paper we report on the first observation of positronium formation in a large liquid scintillator detector based on pulse shape analysis of single events. The o-Ps formation fraction and its lifetime were measured, finding the values of 44$\%$ $\pm$ 12$\%$ (sys.) $\pm$ 5$\%$ (stat.) and $3.68$ns $\pm$ 0.17ns (sys.) $\pm$ 0.15ns (stat.) respectively, in agreement with the results obtained with a dedicated positron annihilation lifetime spectroscopy setup.